1) Field
Embodiments of the present invention pertain to the field of semiconductor processing and, in particular, to methods and apparatuses for outgassing materials.
2) Description of Related Art
In a plasma process, accurate control of the vacuum pressure and the flow rate of processing gasses are needed to ensure that a plasma with the desired characteristics is obtained. For example, the pressure and flow rate of processing gasses may be chosen in order to optimize an etch rate in a plasma etching process. However, materials that are being processed in the chamber may outgas when subjected to the low pressures in a plasma process. The outgassed substances may alter the properties of the plasma. For example, in a plasma etching operation, outgassing from the material being processed may decrease the etch rate. The decreased etch rate reduces the throughput of the vacuum chamber. Furthermore, without the ability to control the outgassing, the repeatability of the process may be reduced since some workpieces may outgas more than others.
Accordingly, materials that will be processed in a vacuum chamber are carefully selected for their outgassing properties. Materials with low leak rates are needed in order to ensure that outgassing is minimized. For example, polymers and adhesives typically have high leak rates and are generally not used in plasma processing operations. Attempts to control the outgassing of high leak rate materials may include the use of a hard bake to drive off some of the gasses or liquids, such as water, that may be retained by the material. However, moisture may absorb or adsorb back into the material when the temperature of the workpiece is reduced after the hard bake. As such, there may still be retained gasses or liquids in the material that may outgas when the workpiece is processed in a plasma processing chamber.